Safety means for well flow control

ABSTRACT

Two self-contained, subsurface operated, subsurface safety valves are positioned at vertically spaced locations within a well production tubing. The upper valve closes automatically when the tubing pressure falls below a predetermined low value and the lower valve closes automatically when the tubing pressure rises above a predetermined high value. The system is surface operated by closing the wellhead which permits the tubing pressure to rise to the high value, closing the lower valve. Reopening the wellhead permits the tubing pressure to drop to the low value, closing the upper valve. The valves may also be remotely or surface operated by dropping the wellhead pressure to the low pressure value which closes the upper and then the lower valves. Both valves also close automatically when well damage permits uncontrolled well flow which causes tubing pressure to drop to the low value. If well damage terminates or limits flow, the tubing pressure rises to automatically shut in the high pressure valve. Both valves may be reopened by pressuring from the wellhead. The preferred form of the high pressure valve of the present invention includes means for reopening the valve by increasing the wellhead pressure above that required to close the valve. For this purpose, a pressure sensitive actuator in the valve is reengagably detachable from the valve closure elements. The invention includes methods for automatically or remotely closing a well, for reopening the well, and for testing valve operation. A modified form of the invention employs flow rate responsive valves rather than pressure responsive valves. In the modified form, one valve closes when the flow exceeds a predetermined rate and the other valve closes when the flow drops below a predetermined rate.

United States Patent Brown et a1.

[ SAFETY MEANS FOR WELL FLOW CONTROL Primary Examiner.lames A. Leppink Attorney, Agent, or Firm-Trres and Berryhill [57] ABSTRACT Two self-contained, subsurface operated, subsurface safety valves are positioned at vertically spaced locations within a well production tubing. The upper valve closes automatically when the tubing pressure falls below a predetermined low value and the lower valve closes automatically when the tubing pressure rises above a predetermined high value. The system is sur- Mar. 26, 1974 face operated by closing the wellhead which permits the tubing pressure to rise to the high value, closing the lower valve. Reopening the wellhead permits the tubing pressure to drop to the low value, closing the upper valve. The valves may also be remotely or surface operated by dropping the wellhead pressure to the low pressure value which closes the upper and then the lower valves. Both valves also close automatically when well damage permits uncontrolled well flow which causes tubing pressure to drop to the low value. If well damage terminates or limits flow, the tubing pressure rises to automatically shut in the high pressure valve. Both valves may be reopened by pressuring from the wellhead.

The preferred form of the high pressure valve of the present invention includes means for reopening the valve by increasing the wellhead pressure above that required to close the valve. For this purpose, a pressure sensitive actuator in the valve is reengagably detachable from the valve closure elements.

The invention includes methods for automatically or remotely closing a well, for reopening the well, and for testing valve operation.

A modified form of the invention employs flow rate responsive valves rather than pressure responsive valves. 1n the modified form, one valve closes when the flow exceeds a predetermined rate and the other valve closes when the flow drops below a predetermined rate.

35 Claims, 8 Drawing Figures SAFETY MEANS FOR WELL FLOW CONTROL BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to means for controlling the flow of petroleum fluids through an oil or gas well. More specifically, the present invention relates to subsurface controlled subsurface safety valves, and surface controlled, subsurface safety valves operable to 1 close automatically when predetermined well conditions exist, or to be closed at any time by remote, surface operations conducted at the wellhead. The field of the present invention relates also to specific sursurface valve apparatus and to methods employed in closing wells and to methods employed in testing for proper closure of subsurface valves.

2. Brief Description of the Prior Art In a conventional automatic well control system, a single subsurface operated, subsurface safety valve is disposed within the production tubing of the well. The subsurface valve is normally designed to close automatically when predetermined pressure or flow conditions exist within the well. Normally, the subsurface valve closes automatically when the tubing pressure drops below a predetermined minimum value or when the rate of fluid flow through the tubing increases above a predetermined maximum value. Either of the latter two situations normally correspond to uncontrolled flow of well fluids through the production tubing string caused by damage to or inoperability of the well structure above the subsurface valve.

Offshore oil and gas wells are particularly susceptible to wellhead damage caused, for example, by collision with vessels or by violent storms. Automatic subsurface safety valves have been required for such offshore wells to prevent fire and property damage and to prevent pollution of the water and air caused by the uncontrolled flow of petroleum fluids through the well following damage to the well structure. The valves must be positioned at a subsurface location which is relatively protected from surface accidents and fire.

Surface controlled or remotely operated subsurface safety valves have also been employed to prevent uncontrolled well flow in offshore well installations. Typically, such surface operated safety valves include a small hydraulic line or macaroni string which extends between the subsurface valvelocation and the well surface. Hydraulic pressure in the line is employed to regulate opening and closing of the subsurface valve. Normally, the subsurface valve operates to close automatically in the event pressure is lost in the small hydraulic line.

Often, with prior warning of impending danger such as an approaching hurricane or a fire on an adjacent or nearby well structure, it is desirable to positively closein the surface and the subsurface valves in a well as soon as possible. If the subsurface valve does not close automatically, damage to the wellhead caused by the storm or fire would permit the well to flow uncontrollably or to leak. This danger can be reduced by closing in the subsurface valve before the fire or storm strikes.

Surface operated subsurface valves are preferable to subsurface operated subsurface valves in that the former may be closed easily by simple surface operations. Conventional subsurface operated, subsurface valves are not well suited for surface control in that they require an undesirably high rate of surface flow to effect valve closure. In many cases, it is not possible to drop the tubing pressure by permitting high surface flow from the wellhead since the offshore well instalation may have no provision for accommodating the high volume of well fluids required to drop the pressure in the tubing sufficiently for automatic closure of the subsurface valve. Even where it is possible to flow the well at the rate required to test the valve, such practice is undesirable in that the high rate of flow may cause the 0 well to sand-up or otherwise cause damage to the subsurface formation. While providing positive surface controlled closure, surface operated, subsurface safety valves employing a separate hydraulic line are objectional because the small hydraulic line is difficult to install and retrieve, and because the line is subject to breakage, crimping or other damage which may render the valve inoperative.

It is also desirable to test subsurface valves periodically to ensure that they are operating properly. Surface operated, subsurface safety valves may be easily tested by performing the necessary surface action. Subsurface operated, subsurface safety valves cannot, however, be so easily tested since the closure requires the objectionable high volume wellhead flow. For this reason and others, the valves must be periodically removed from their subsurface location, checked, repaired if necessary, and then repositioned. The latter operation may require the use of a special crew and also involves a significant loss in well production time.

A primary difficulty associated with'the typical prior art subsurface operated, subsurface safety valve is that the valves fail to close where the production tubing pressure remains high but leakage occurs through damages or inoperative portions of the well structure above the valve. Such leakage occurs for example where several wells are mounted on a single offshore structure and the heat from one of the burning wells warps or otherwise damages the other well structures causing leakage of well fluids through the damaged structures. Where such leakage occurs on an offshore platform, it will be appreciated that the fuel will feed the fire for indefinite periods of time even though the well is not freely flowing. A similar leaking situation occurs for example where a hurricane knocks over the structure causing the tubing and casing strings to bend and crack. Any resulting leakage permits oil and gas to leak into the water causing undesirable pollution.

In an effort to terminate leakage from damaged wells, the wellhead has been destroyed with explosives to initiate the required high volume flow and subsequent pressure reduction required to automatically shut in the subsurface valve. There is a significant danger, however, that the subsurface valve would fail to operate and the leaking well would be converted to an even less desirable, uncontrolled blowinG well.

SUMMARY OF THE INVENTION The present invention includes a system in which two separate subsurface safety valves are employed in a given production tubing string to prevent the uncontrolled flow of fluids through the well. In the preferred form of the system, the upper valve closes automatically when the tubing pressure drops below the normal flowing pressure of the controlled well. The lower valve closes automatically when the pressure in the tubing string rises above the normal flowing pressure of the well. Each of the valves is subsurface operated in that Hobo they close automatically in response to subsurface well conditions. The valves are also remotely or surface operated without high volume surface flow by first closing the wellhead to permit the tubing pressure to rise to the high pressure cut off level which closes the high pressure valve. By reopening the wellhead, the tubing pressure falls to the point required to cause closure of the low pressure valve. The wellhead may then be reclosed and the well is shut in on two subsurface valves and the wellhead valve.

If the wellhead is damaged causing a restriction in the tubing string which either completely terminates flow through the tubing string or permits small amounts of the well fluid to leak, the resulting high pressure in the tubing string causes the subsurface valve to close automatically to prevent further leakage. lf the wellhead structure is ruptured, so that the well flows at a high rate, the low pressure valve shuts automatically to completely terminate flow. In the latter situation, the high pressure valve will close following closure of the low pressure valve when the tubing pressure below the low pressure valve rises to the high pressure cut off valve.

ln the preferred form of the invention, the high and low pressure valves may be reopened for subsequent automatic closure by pressurizing the tubing string from the wellhead. The valves are also preferably retrievable so that they may be removed from the well conduit and subsequently repositioned without the need for removing the conduit from the well.

Proper operation of the valve may be tested by first closing the wellhead structure to cause closure of the high pressure valve. Subsequent opening of the wellhead permits the tubing pressure to drop to the point required to close the low pressure valve. Closure of the high pressure valve may be verified by monitoring the wellhead pressure and closure of the low pressure valve may be verified by monitoring the rate of wellhead pressure change with the wellhead partially open and the high pressure valve closed. As an alternative method for checking closure of the two valves, the wellhead may be closed permitting the pressure in the tubing string to rise to the high cut off pressure. When the wellhead is reopened, the absence of fluid flow verifies closure of the high pressure valve. Thereafter, the wellhead may be repressured to cause reopening of the high pressure valve and then, where facilities permit, the wellhead pressure may be permitted to drop to the point required to cause closure of the low pressure valve with closure being verified by termination of flow at the wellhead. The first testing method is preferable in that it does not require high wellhead flow to establish the low pressure required in closing the low pressure valve.

The preferred form of the high pressure valve employed in the present invention includes means for separating the actuating control mechanism from the closure element of the valve by pressurizing the wellhead with the high pressure valve closed. In one form of the invention, the actuator and closure means are separated at a wellhead pressure which is below the formation pressure. After separation, the wellhead pressure is increased to the point necessary to equalize the differential across the closed valve which permits a spring biasing force to snap the valve back into its open position. A subsequent reduction in wellhead pressure, below the high pressure close value, and preferably to the normal flowing pressure of the well, causes the actuator and closure member mechanism to reattach so that the high pressure valve is prepared to automatically reclose. In another form of the invention, the actuator and closure means separate when the wellhead pressure exceeds the formation pressure. Once separation occurs, the valve snaps open under the combined influence of the resulting pressure differential across the closed valve and the force of a compressed opening spring. Both forms of the high pressure valve permit closure of the valve in the presence of a given tubing pressure and also permit reopening of the valve when higher pressure is applied from above the closed valve. By this means, the high pressure valve may be remotely reopened without the need for surface operated wireline equipment or other surface connected apparatus.

From the foregoing, it may be appreciated that one of the primary objects of the present invention is to provide a system having subsurface controlled, subsurface safety valves which may be remotely or surface operated for controlling the flow of fluids through a well.

Another object of the present invention is to provide a system in which subsurface valve operation may be verified by surface operation.

Another object of the present invention is to provide a system in which two subsurface valves automatically close in the event of uncontrolled well flow.

Still another object Of the present invention is to provide a system in which the subsurface valves may be quickly and easily closed without the need for special facilities required to accommodate large volume surface flow.

It is also an object of the present invention to provide a surface operated system which may close and open subsurface valving means in a production tubing without the need for mechanical means connected between the valve and the surface and without the need for small hydraulic control lines or other structures extending between the subsurface valve and the surface.

Still another object of the present invention is to provide an automatic well control system employing retrievable subsurface valves where such valves are subsurface operated and may also be surface operated.

An important object of the present invention is to provide a system having subsurface valves which may be reopened by pressure supplied from the wellhead to permit subsequent automatic reclosure of the subsurface valves.

Also an object of the present invention is to provide a subsurface safety valve which is automatically closed when the tubing pressure exceeds a predetermined maximum value and which can be reset by pressure applied to the tubing from the wellhead.

In its broader aspects, the present invention provides dual, subsurface controlled subsurface valves which close automatically in response to subsurface conditions corresponding to uncontrolled well flow, whether such flow be unrestrained flow from the well or leakage from a well where flow is restricted by valves or damage to the well structure. While pressure responsive valves are preferred, the subsurface valves may be responsive to flow rate, pressure or any other characteristics of the well fluids which show the well condition.

The foregoing features, advantages, and objects of the present invention may be more fully understood from the following specification, claims and the related drawings.

BRIEF DESCRIPTION OF THE DRAWINGS In the description which follows, reference will be made to the accompanying drawings in which:

FIG. 1 is a schematic representation of a pressure responsive well control system having a high pressure safety valve and a low pressure safety valve according to a preferred embodiment of the invention;

FIG. 2 is a sectional, vertical elevation of the high pressure safety valve of the preferred form of the invention showing the valve in its normally opened position;

FIG. 3 is a view similar to FIG. 2 showing the valve in a position in which the closure member has just been released for movement toward a closed position;

FIG. 4 is a view of the safety valve of FIGS. 2 and 3 illustrating the valve in its closed position prior to the release of an actuating control bellows from the valves closure member;

FIG. 5 illustrates the valve in the closed position following the release of the control bellows from the closure member;

FIG. 6 is a horizontal cross-section view taken along line 66 of FIG. 2, illustrating details of the locking mechanism employed for maintaining the closure member in its open position;

FIG. 7 is a horizontal cross-sectional view taken along line 7-7 of FIG. 5 illustrating the locking mechanism of FIG. 6 in the disengaged position in which the closure member is freed for movement to the closed position; and

FIG. 8 is a schematic representation of a flow rate responsive system according to a modified form of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 schematically depicts the preferred form of the safety valve system of the present invention in a production well conduit 10 which forms part of a conventional well structure W. The upper end of the structure W is equipped with a conventional Christmas tree" or production manifold which includes a valve 12. The lower end of the structure W is in fluid communication with a subsurface petroleum bearing formation (not illustrated) and is equipped with a packer (not illustrated which causes the formation effluents to flow through the well conduit 10 in a conventional manner.

A decreased or low pressure valve 20 is installed in the conduit 10 at a subsurface location within the well W. Installed at some point below the valve 20 is an increased or high pressure safety valve 50. In offshore wells, the valves 20 and 50 are normally positioned at a point below the water bottom or mudline where they are less likely to be damaged by surface events. The low pressure valve 20 may be any valve designed to close automatically when the pressure in conduit 10 falls below a preselected low pressure level which is below the normal controlled flowing pressure of the well. The valve 50 may be any valve designed to close automatically when the pressure in tubing 10 rises to a preselected high pressure level which is above the normal controlled flowing pressure of the well. When the pressure of the fluid in conduit 10 is between the preselected high and low values, the valves 20 and 50 remain open.

Placement, setting and retrieval of both the valve 20 and the valve 50 may be effected by wireline techniques, hydraulic pumping, tubing manipulation or other suitable means. Where retrievable valves are employed for the valves 20 and 50, the valves may be anchored in specially configured landing mandrels included as a part of the conduit 10, or they may be locked in a collar recess between adjoining conduit sections, or they may be anchored to the internal conduit walls by conventional frictions slips, or they may be temporarily secured within the conduit 10 by any other suitable means. It should be noted that while retrievable valves are preferred in the practice of the present invention, the valves may be a fixed part of the conduit string.

While any suitable valve may be used for the valve 20, the valve is preferably of the pressure protected bellows type described in U. S. Pat. application Ser. No. 153,617, filed June 16, 1971, and entitled AUTO- MATIC SAFETY VALVE. The low pressure valve 20 may include an anchoring and sealing assembly 22 carried on a valve body 30. The assembly includes an anchoring means 22a which anchors the valve at a desired subsurface location within the well conduit 10 and a sealing means 22b which forms a seal between the well conduit and the valve body to prevent fluid in the conduit from flowing axially past the valve 20 without first flowing through a valve flow passage 31.

The low pressure valve 20 is provided with a seating surface 32 surrounding the flow passage 31 and a closure member 33 adapted to move into engagement with the seating surface 32 to block flow through the flow passage 31. The closure member 33 is connected through a stem member 34 to an extensible and contractable pressure bellows 40 which forms a portion of the automatic control apparatus employed for opening and closing the valve. The internal area confined by the pressure bellows 40 is filled with an incompressible fluid such as oil or other suitable liquid and is in pressure communication with a pressure dome or chamber 51 containing a compressible fluid, such as nitrogen or other suitable fluid. The bellows 40 is preferably equipped with a suitable bellows protection means (not illustrated) which prevents high tubing pressure or high dome pressure from damaging the bellows. Details in the construction of a valve having all of the features described for the valve 20 are given in the previously mentioned patent application Ser. No. 153,617.

The bellows 40 is normally contracted and holds the closure member 33 in the open position shown in FIG. 1. When the pressure within conduit It) falls below the predetermined low pressure level, the bellows 40 extends and moves the stem 34 upwardly which permits disengagement of a lock mechanism 42 securing the closure 33 to the valve body 30. Once the mechanism 42 disengages, a compressed coil spring 42a snaps the closure member 33 into engagement with the seat 32 to block flow through the passage 31. The valve 20 is returned to its original open position by pressuring the well conduit 10 above the valve.

The high pressure valve 50 may be any valve capable of closing when the tubing pressure exceeds the predetermined high pressure value. The general operation and construction of a preferred form of the high pressure valve 50 are depicted schematically in FIG. 1. The valve 50 includes an anchoring and sealing assembly 60 which includes conventional anchoring means 60a and conventional sealing means 60b. A tubular body 55 in the valve 50 is provided with a fluid inlet and a fluid outlet connected by an annular flow passage 59 around which is provided an annular seat 57. A closure member 70 and a control assembly 80 connected to the closure member 70 respond to a high pressure within the conduit 10, above the predetermined high pressure level, to seat the closure member 70 against the seat 57 blocking flow through the valve 50. Thus, lower safety valve 50 closes when the pressure exceeds a given high valve while the upper safety valve 20 closes when pressure drops below a given low value. Normal well flow is maintained through the conduit 10 when the pressure acting against the valves 20 and 50 is in the normally expected range between the high and low pressure values.

In operation, the low pressure valve 20 will close automatically if the well structure is damaged or destroyed causing uncontrolled flow through the conduit 10 since the pressure in the conduit will drop below the low pressure cut-off value. In the event damage to or malfunction of the well structure restricts conduit flow above the valve 50, the pressure in the conduit will rise to the high pressure cut-off value to close the valve 50. The valve 50 thus functions to cut off flow where conduit damage or malfunction permit slow seepage of the high pressure effluent in the conduit. The combined use of a high and a low pressure valve provides a system in which high pressure seepage or leaking is prevented, uncontrolled high flow is prevented and in which remote, surface control may be employed to shut in the well on two subsurface valves.

The subsurface safety valves 20 and 50 are subsurface operated since they respond automatically to the pressure existing in the well conduit. The two valves may also be surface operated by first closing the well conduit 10 at a point above the valve, usually at the surface by closing the valve 12. The formation pressure causes the pressure in the conduit 10 to rise above the high pressure level which causes the valve 50 to close and block the conduit. With the valve 50 closed, the surface valve 12 may then be reopened to permit the pressure acting on the valve 20 to fall below the pressure value which in turn causes the valve 20 to close. it will be appreciated that with the valve 50 closed, the pressure in the conduit 10 is dropped without the high volume wellhead flow normally required to shut in a well equipped only with a single flow pressure safety valve. When the valves 20 and 50 are closed, the surface valve 12 may be closed and the well structure is shut in on two subsurface valves and on the wellhead.

Once closed, the valves 20 and 50 remain closed unless positively reopened by surface operations. As will be explained hereafter in greater detail, the valves 20 and 50 are reopened by applying pressure to the conduit 10 above the two valves until the upper valve 20 opens and the control assembly 80 in the valve 50 disconnects from the closure member 70. In one form of the invention, the disconnect and the opening pressures are the same and the valve snaps open when the assembly 80 and member 70 disconnect. In another form, the assembly 80 disconnects from the closure member 70 when the wellhead pressure is raised to a value below the formation pressure. Complete opening of this form of the valve requires that the pressure above the valve 50 be raised further until the pressures above and below the valve are substantially equal allowing the closure member to return by spring biasing to the open position shown in FIG. 1. In both valve forms, with the valve 50 open and the assembly and closure 70 separated, normal flow is permitted to resume causing the tubing pressure to be reduced to the normal flowing pressure level of the well permitting the control assembly 80 to reconnect with the closure member 70 so that the valve 50 is again capable of automatically closing when the high pressure value reoccurs.

For testing purposes, closure of the valves 20 and 50 may be readily verified by monitoring the pressure in conduit 10 at the wellhead. When the wellhead valve 12 is initially closed, a pressure and rate indicator P will show that the pressure in the conduit 10 rises to substantially the high pressure value and then remains constant, thus verifying closure of the high pressure valve. If the high pressure valve fails to close, the wellhead pressure will rise a recognizable amount above the high pressure value and on reopening of the valve 12, the well effluents will flow from the wellhead. When the valve 50 functions properly and closes, the valve 12 may be opened to relieve the pressure in the conduit 10 and the indicator P will show the tubing pressure decline at a steady rate until the valve 20 closes which will cause the pressure to decline at a faster rate. Failure of the valve 20 to close is evidenced by the absence of an increased pressure decline rate at the wellhead. lf desired, the indicator P may be associated with means for recording the pressure change at the wellhead so that an operator may examine the recording after the well has closed in to determine if both valves closed. The difference in the pressure decline upon closure of the valve 20 is due to the fact that the volume of pressun ized fluids acting at the wellhead is greater with the valve 20 open then it is with the valve 20 closed. The extra volume of fluids contained between the upper and lower valves produces a measurable pressure characteristic at the wellhead when the extra volume is acting through the open valve 20 with the valve 12 open. With the valve 20 closed, a smaller volume acting at the wellhead causes a more rapid drop in pressure. The valves 20 and 50 are preferably spaced vertically sufficiently to include between them the volume required to show a measurable pressure change at the wellhead when the upper valve closes following closure of the lower valve. verified,

The entire system may also be tested by first shutting the well in and allowing pressure to build up to the high level necessary for closing the high pressure safety valve 50. Once closure of the valve 50 is verified, the wellhead pressure is further increased to reopen the valve 50. Subsequent reduction of pressure preferably to the normal flowing pressure of the well, reconnects the bellows unit and a further reduction of pressure verifies closing of the low pressure valve 20.

Referring now to FlGS. 2-7, a preferred form of the high pressure safety valve 50 will be described in detail. As previously described, the valve 50 includes a tubular valve body 55 which is anchored within the well conduit by an anchoring and sealing means 60 (only a portion of which is shown in FIG. 2) which may be connected to the valve body 55 by any suitable means, such as a threaded adaptor 61. The anchoring and sealing assembly 60 may be of any suitable design for retrievably anchoring the valve body 50 at a subsurface location within the conduit and for forming a seal between the conduit and the valve body 55 to prevent fluids in the well conduit from flowing axially past valve 50 without first flowing through the annular flow passage 59.

The seat 57 surrounding the flow passage 59 may be carried on a suitable seat member 62 which is retained within the valve body 55 by a threaded collar 65. A seal member 66 provides a seal between the seat member 62 and the valve body 55. Also carried by the valve body 55 is the control assembly referred to generally by reference numeral 80. The control assembly 80 is centrally disposed within the valve body 50 to form the annular flow passage 59. The central location of the assembly 80 is maintained by a plurality of centralizer lugs 81 which may be welded to the control assembly 80 leaving a fluid flow space between the assembly and the body 55. The centralizer lugs 81 are anchored in a recess formed between an annular shoulder 82 in the valve body 55 and an upper axial end 68 of the seat member 62. The control assembly 80 includes a composite cylindrical housing made up of four sections 84, 85, 86 and 87 as shown in FIG. 2.

Telescopically received in the lower section 84 of the control housing, for limited axial movement therein, is a stem assembly which includes an upper cylindrical guide member 91, an intermediate member 92 and a lower member 93 which may be connected to or form an integral part of the closure member or disc '70. The lower stem section 93 along with the closure member 70 is maintained in a fixed axial position relative to the valve body 55 by a locking mechanism which may include a plurality of locking balls 95 carried in radial holes 96 formed in the wall of the lower stem section 93. In their radially outermost position, (see (FIG. 6) the locking balls 95 engage and lock with an annular groove 98 formed on the interior of the lower control housing section 84. The balls 95 are maintained in locked position in the groove 98 as long as the intermediate stem section 92 is in the position of FIG. 2, preventing radial retraction of the balls 95. The upper and intermediate stem sections 91 and 92 are biased downwardly toward the position of FIG. 2 by a coil spring member 100. It will be appreciated that the stem section 93is locked so that small pressure changes and well flow can not cause the stem to move away from the full open position.

The stem assembly is attached through a bellows adaptor 110 to a contractable and extensible bellows unit 112 which forms part of the control assembly 80. The bellows unit 112 is secured at its upper end to housing section 86 while the lower bellows end is free to move axially between defined limits within the housing section 85. For a purpose to be described hereafter, the bellows adaptor 110 is attached to the stem assembly by a disengagable and reengagable locking mechanism such as provided for example by collet fingers 113 illustrated in FIG. 2. The collet fingers 113 are formed by a plurality of circumferentially spaced, axially disposed members which extend downwardly from the tubular body of the adaptor 110. The fingers are constructed of a resilient metal which urges lugs 114 radially inwardly into an annular groove 115 formed around the intermediate stem section at the lower end of the fingers 91. Thus, the stem assembly will follow the contraction or extension of bellows unit 112 when the collet finger lugs 114 are latched in the stem groove The internal area of the bellows unit 112 is filled with a noncompressible fluid such as oil or other suitable liquid, and is adapted to communicate with a pressure dome or chamber containing a compressible fluid, such as nitrogen or other suitable fluid. Resting atop the upper end of the bellows adaptor 110 is a bellows protection unit which includes a seal member 131 and a tubular alignment member 131a. The member 131 is equipped with an annular, resilient seal ring l31b' adapted to seat against frusto-conical seating surfaces of 141. Unless the sealing ring 131b is sealingly engaging one of the seating surfaces 140 or 141, pressure communication is maintained between the bellows unit 112 and the pressure chamber 120.

The bellows protection unit 130 also includes a guide rod or stem 134 which reciprocates in a guide hole in the upper end of a guide cap or sleeve 136 threadingly and sealingly connected to the housing section 86. The protection unit 130 is biased downwardly by a coil spring member 138. It will be noted that the alignment member 131a forming the lower portion of bellows protection unit 130 is provided with ports 139 which permit the incompressible fluid to enter the member to ensure complete absence of compressible fluids in the bellows unit 112. A filling valve 148, covered by a protective cap 149 is provided at the upper end of the housing section 87 for charging the pressure dome 120. The bellows protection seal ring 131b seats against the seat 140 to permit the chamber 120 to be charged to a high pressure without over distending the bellows. When the seal ring 131b seats against the upper seat 141, the incompressible fluid filling the bellows 112 is trapped and high pressure acting externally of the bellows is prevented from over compressing the bellows.

In operation, as long as the pressure in the well conduit 10 is below the high pressure level, the closure member 70 is maintained in the open position of FIG. 2. To close the valve, it is necessary to raise the pressure of the fluids within the conduit 10 above the high pressure level. This may be accomplished remotely by closing a valve at the surface of the well and allowing the conduit pressure to build toward the formation pressure. As the predetermined high pressure level is approached, pressure is transmitted to the exterior of bellows unit 112 through ports 85a formed in housing section 85 causing the bellows unit 112 to be contracted, compressing the compressible fluid within the dome 120.

Contraction of the bellows unit 112 raises the intermediate stem section 92 as shown in FIG. 3, until a reduced diameter portion of the section registers with the locking balls 95. At this point, the balls 95 are permitted to retract radially to disengage the groove 98 which permits the stem section 93 and the closure member 70 to move axially upwardly with the contracting bellows. During the initial upward movement of the stem section 92 toward the ball release position, a pin member 150 attached to the section 92 is lifted to the top of a slot 151 in the lower stem section 93. The engagement of the pin 150 with the top of the slot 151 causes the stem section 93 to be moved upwardly with the stem section 92. As the closure member 70 approaches engagement, with the seating surface 57, an opening spring 153 is compressed. Upward movement of the stem sssembly is permitted until a resilient seal ring 70a on closure member 70 engages the seat member 62 as shown in FIG. 4, preventing further upward movement.

The valve 50 is closed at this time and the pressure exerted on the lower side of closure member 70 assists in maintaining the valve in closed position.

When it is desired to reopen the safety valve 50, in one form of the invention, it is necessary to pressurize the conduit above the valve 50 to a pressure which is lower than the formation pressure and slightly higher than the pressure required to close the valve 50. For example, if 2,000 psi is required to close the valve, a pressure of 2,100 psi may be applied to the conduit above the valve. The reopening pressure acts on the exterior of the bellows unit 112 through ports 85a causing the bellows unit to be further contracted. Since the stem assembly is prevented from further upward movement by engagement with the seat 62, the collet finger lugs 114 are forced out of engagement with groove 115, disconnecting the bellows adaptor 110 from the stem assembly. This is best seen in FIG. 5. When the valve 50 moves to this latter position, the bellows protection unit seal ring l3lb sealingly engages the upper seat 141 which traps the fluid in the bellows to prevent damage to the bellows unit which might be caused by further bellows contraction. Since the stem assembly and closure member 70 are no longer operatively linked to the bellows unit 112, the valve may be opened by increasing the wellhead pressure further to equalize the pressure on either side of closure member 70. With pressures equalized, the closure member will be returned to the open position (illustrated in FIG. 2) by expansion of the compressed opening spring 153.

To reconnect the bellows adaptor 110 and bellows unit 112 to the stem assembly, it is necessary to reduce pressure within the well conduit to a pressure level sufficient to allow extension of the bellows unit, compression of the spring 100 and reengagement of the collet fingers 113 with the locking groove 115. This may preferably be accomplished by opening the tubing at the surface of the well and allowing the well fluids to flow at the normal rate to reduce the tubing pressure to the normal flowing pressure level of the well.

The separation force required to part the control assembly 80 from the closure member 70 is preferably adjustable so that if desired, the valve 50 may be adjusted to cause separation of the control assembly and closure member only when the pressure above the closed valve is higher than the pressure below the valve. When the desired differential is established, the closure member automatically snaps open under the combined influence of the opening spring and the pressure differential across the closed valve. The closure 70 and the control assembly 80 are reengaged by reducing the well pressure to the normal flowing pressure. Valves adjusted to separate the control 80 from the closure 70 when the pressure above the valve is greater than that below are desirable where there is a danger that the closed valve will leak causing the pressures above and below the valve to equalize leak which in turn would permit the valves adjusted to operate in the manner described previously to reopen.

An important feature of the exemplary forms of the high pressure valve 50 forming a part of the present invention is that they automatically close in the presence of unusually high pressure, but may also be recocked or reopened for subsequent automatic operation by applying pressure from the well surface. In the preferred form of the high pressure valve 50, the reopening capability is provided by the releasable and reengageable connection between the valve control and the valve closure elements.

In a preferred method of the present invention, the high pressure valve is first closed by closing the wellhead until the necessary high pressure is obtained and the low pressure valve is subsequently closed by reopening the wellhead until the necessary low pressure is obtained. With both valves closed, the danger of leakage past the safety valves is significantly reduced. By the use of this method, the well may be positively shut-in on two separate subsurface valves by remote or surface control. As an additional step in the method of the invention, the subsurface valves may be reopened by pressurizing the well tubing from the wellhead.

While the present invention has been described with reference to pressure sensitive subsurface valves which are preferred, it will be understood that flow rate sensitive valves may be employed. A flow rate responsive system W is depicted schematically in FIG. 8. In the system of FIG. 8, a subsurface valve closes when the flow rate of the well fluids through a production conduit exceeds a predetermined maximum value corresponding to uncontrolled flow through the well. A second valve closes when the flow rate drops below a predetermined minimum rate corresponding to closure or restriction of the tubing 115. Any suitable means, pressure responsive or otherwise, may be employed in the flow responsive valves 110 and 120 to permit valve reopening following repair of the well damage or completion of the testing. The system W would also be surface controlled without undue surface flow in that closure of the wellhead (not illustrated) would cause closure of the low flow rate valve 120. In the event the high flow rate valve 110 closes first, the low flow rate valve will also close automatically so that the well is shut-in on two valves.

Although specific exemplary embodiments and operations of the invention have been described herein, many variations thereof will be apparent to those skilled in the art. Thus, while the controls or actuators for the valves 20 and 50 were described as being bellows" operated, it will be appreciated that the bellows function may be performed by a rigid piston moving through a cylinder or by other suitable means. Although not the preferred form of the present invention, it may be desired to position the high pressure valve above the low pressure valve. With the latter modification, only the low pressure valve closes when the tubing pressure drops and the high pressure valve remains open. While some applications of the present invention may require such operation, the preferred form is with the high pressure valve below the low pressure valve so that both valves close when the low pressure valve closes. Other modifications will also be apparent and it is therefore intended that the scope of the invention be limited only by the claims which follow.

We claim:

1. A method of remotely or automatically operating valve means and control means anchored in a well conduit at a point below the surface of a well comprising the steps of:

a. partially or completely closing said well conduit above said valve and control means;

b. allowing the pressure in said conduit to rise to a first pressure level to which said control means is automatically responsive for closing said valve means and blocking said conduit; and

0. raising the pressure in said conduit above said valve means to a second pressure level higher than said first level whereby said control means is operatively disconnected from said valve means.

2. A method as defined in claim 1 and the additional step of:

d. raising the pressure in said conduit above said valve means to a third pressure level higher than said second level whereby the pressures above and below said valve means are substantially equal allowing said valve means to be opened.

3. A method as defined in claim 3 and the additional step of:

e. reopening said well conduit above said valve and control means and allowing the pressure in said conduit at said valve means to fall to a fourth pressure level lower than said first pressure level whereby said control means is operatively reconnected with said valve means.

4. A method as defined in claim 1 wherein said second level is higher than the pressure below said valve means.

5. A method as defined in claim 3 in which said well conduit is partially or completely closed above said valve and control means by manipulating the valve near the surface of said well.

6. A method as defined in claim 4 in which a second valve and control means are anchored in said conduit at a point between the first mentioned valve and control means and the surface of said well, and said well conduit is closed above said first valve and control means by lowering the pressure in said conduit above said second valve means to a level below said first pressure level to which said second control means is automatically responsive for closing said second valve means and blocking said conduit.

7. An automatic safety system for terminating flow through a well conduit included in a well comprising:

a. first valve means anchored in said well conduit at some point below the surface of said well, said first valve means including means for terminating flow through said conduit in response to pressures below a first pressure level in said conduit; and

b. second valve means anchored in said well conduit at some point below said well surface, said second valve means including means for terminating flow through said conduit in response to pressures in said conduit above a second pressure level, higher than said first level.

8. An automatic system as defined in claim 7 wherein said second valve means further includes reopening means for reopening said second valve means in response to pressures in said well conduit above said second pressure level.

9. An automatic system as defined in claim 7 wherein said second valve means is anchored in said well conduit at a point below said first valve means.

10. An automatic system as defined in claim 9 wherein:

a. said second valve means includes a closure member, a seat member and a self-contained control means; and

b. said self-contained control means is connected to said closure member and responsive to said second pressure level to bring said closure and seat members into sealing engagement with each other for blocking flow through said conduit.

11. An automatic system as defined in claim 9 wherein said first and second valve means are movable through said conduit and include means for retrievably anchoring and sealing said valve means at a subsurface location within said well conduit.

12. An automatic system as defined in claim 9 wherein said first and second valve means include reopening means for moving said valve means to open position in response to pressure supplied to said well' conduit above said valve means.

13.An automatic system as defined in claim 10 wherein said self-contained control means includes bellows actuator means for opening and closing said closure members to respectively permit or terminate flow through said conduit.

14. An automatic system as defined in claim 13 wherein said bellows actuator means is linked to said closure member by releasable locking means for operatively disconnecting said closure member from movement of said bellows actuator means in response to pressures in said well conduit above a third pressure level higher than said second pressure level.

15. An automatic system as defined in claim 1 wherein said bellows actuator means further includes relocking means for reengaging said closure member in response to a reduction of pressure in said conduit to a level below said second pressure level.

16. An automatic safety valve means for regulating flow through a well conduit comprising: i

a. closure means movable between open and closed positions for respectively permitting or terminating flow through said conduit;

b. movable control means connected through connecting means with said closure means for moving said closure means between open and closed positions;

0. closing means included with said control means for closing said closure means when the pressure acting on said control means exceeds a first predetermined value; and

d. reopening means included with said control means for reopening said closure means when the pressure acting on said control means is raised above said first pressure value and exceeds a second higher pressure value.

17. An automatic safety valve means as defined in claim 16 wherein said valve means is movable through said conduit and includes means for retrievably anchoring said valve means at a subsurface location within said well conduit.

18. An automatic safety valve means as defined in claim 17 further including spring biasing means for urging said closure members toward open position when said closure means are closed.

19. An automatic safety valve means as defined in claim 17 further including locking means for maintaining said valve closure means in fully opened position while the pressure acting on said control means is below said first pressure value.

20. An automatic safety valve means as defined in claim 19 wherein said valve means is movable through said conduit and includes means for retrievably anchoring said valve means at a subsurface location within said well conduit.

21. An automatic safety valve means as defined in claim 20 wherein said control means includes bellows 22. An automatic safety valve means as defined in claim 21 further including incompressible fluids and protective valving means for protecting said bellows means from over contraction and over expansion.

23. An automatic safety valve means as defined in claim wherein said connecting means includes releasable means for separating said control means from said closure means when the pressure acting on said control means exceeds a second pressure value which is higher than said first value.

24. An automatic safety valve means as defined in claim 23 further including biasing means operative at pressures in excess of a third pressure value, higher than said second value for returning said closure means to open position when said control means and closure means are separated.

25. An automatic safety valve means as defined in claim 24 wherein said connecting means further includes reengageable means for reengaging said control means and said closure means when the pressure acting on said control means falls below said first pressure value.

26. An automatic safety valve means as defined in claim 25 wherein said control means includes bellows means.

27, An automatic safety valve means as defined in claim 26 further including incompressible fluids and protective valving means for protecting said bellows means from over contraction and over expansion.

28. A method of remotely or automatically operating first and second valve means and control means anchored in a well conduit at points below the surface of a well, said second valve and control means being anchored in said conduit at a point between said first valve and control means and the surface of said well, comprising the steps of:

a. partially or completely closing said well conduit above said first valve and control means;

b. allowing the pressure in said conduit to rise to a first pressure level to which said first control means is automatically responsive for closing said first valve means and blocking said conduit; and

c. closing said well conduit above said first valve and control means by lowering the pressure in said conduit above said second valve means to a level, below said first pressure level, to which said second control means is automatically responsive to closing said second valve means and blocking said conduit.

29. A method of controlling flow of well fluids through a well conduit comprising restricting or terminating the flow of well fluid through said conduit at a point above a first subsurface valve which closes in response to a predetermined characteristic of said fluid caused by said restriction or termination of flow, with such method including the prior step of reducing restriction to fluid flow in said conduit at a point above a second subsurface valve which closes in response to a predetermined characteristic of said fluid caused by said restriction reduction, said second valve being located above said first valve whereby said closure of said second valve restricts or terminates fluid flow through said conduit to cause closure of said first valve.

30. A method as defined in claim 29 including the step of reopening said first and second valves by applying pressure to said conduit above said valve.

31. A method as defined in claim 29 wherein said first valve closed in response to the flow of fluids through said conduit at a rate below a first predetermined flow rate and said second valve closes in response to the flow of fluids through said conduit at a rate above a second predetermined flow rate, higher than said first rate.

32. A method as defined in claim 29 wherein said first valve closes when the pressure of fluids in said conduit exceeds a first value and said second valve closes when the fluid pressure drops below a second value, below said first pressure value.

33. A method of controlling the flow of well fluid through a well conduit comprising restricting or terminating the flow of well fluids through said conduit at a point above a first subsurface valve which closes in response to a predetermined characteristic of said fluids caused by said restriction or termination of flow and reopening said first valve by applying pressure to said conduit from above said first valve.

34. A method of controlling flow of well fluids through a well conduit comprising restricting or terminating the flow of well fluids through said conduit at a point above a first subsurface valve which closes in response to the flow of fluids through said conduit at a rate below a predetermined minimum flow rate.

35. A method of controlling flow of well fluids through a well conduit comprising restricting or terminating the flow of well fluids through said conduit at a point above a subsurface valve which closes in response to a predetermined characteristic of said fluids caused by said restriction or termination of flow and reopening said valve by pressurizing said conduit above said closed valve to a pressure in excess of the pressure in said conduit below said valve.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,799, 9 Dated March 26, 197M lnventofls) Joe R. Brown and Joseph L. Johnson It is certified that'error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 2, line 55: change "blowinG" to --blowing.

Column 3, line 22: change "valve" second occurrence to -value. Column I, line 27: change "Of" to -of-. 7 Column 5, line H7: I after "illustrated" insert 82% IE2 It E%I "t fIoSEET- to Column 8, line #6: delete -verified,-.

Column 9, line 33: after "see" delete Column 10, line 11: change "of" to -or.

Column "11, line 57; I after "equalize" delete leak Column 13, line 12: change "3" second occurrence to 2 Column 13, line 27: change I" to --3--.

Signed and sealed this 17th day of September 1974.

(SEAL) Atte'st:

McCOY M. GIBSON JR. c. MARSHALL DANN Attesting Office]: Commissioner .of Patents FORM PO-105O (10-69) 'USCOMM-DC 60376-P69 u.s. GOVERNMENT PRINTING OFFICE I955 O366-334, 

1. A method of remotely or automatically operating valve means and control means anchored in a well conduit at a point below the surface of a well comprising the steps of: a. partially or completely closing said well conduit above said valve and control means; b. allowing the pressure in said conduit to rise to a first pressure level to which said control means is automatically responsive for closing said valve means and blocking said conduit; and c. raising the pressure in said conduit above said valve means to a second pressure level higher than said first level whereby said control means is operatively disconnected from said valve means.
 2. A method as defined in claim 1 and the additional step of: d. raising the pressure in said conduit above said valve means to a third pressure level higher than said second level whereby the pressures above and below said valve means are substantially equal allowing said valve means to be opened.
 3. A method as defined in claim 3 and the additional step of: e. reopening said well conduit above said valve and control means and allowing the pressure in said conduit at said valve means to fall to a fourth pressure level lower than said first pressure level whereby said control means is operatively reconnected with said valve means.
 4. A method as defined in claim 1 wherein said second level is higher than the pressure below said valve means.
 5. A method as defined in claim 3 in which said well conduit is partially or completely closed above said valve and control means by manipulating the valve near the surface of said well.
 6. A method as defined in claim 4 in which a second valve and control means are anchored in said conduit at a point between the first mentioned valve and control means and the surface of said well, and said well conduit is closed above said first valve and control means by lowering the pressure in said conduit above said second valve means to a level below said first pressure level to which said second control means is automatically responsive for closing said second valve means and blocking said conduit.
 7. An automatic safety system for terminating flow through a well conduit included in a well comprising: a. first valve means anchored in said well conduit at some point below the surface of said well, said first valve means including means for terminating flow through said conduit in response to pressures below a first pressure level in said conduit; and b. second valve means anchored in said well conduit at some point below said well surface, said second valve means including means for terminating flow through said conduit in response to pressures in said conduit above a second pressure level, higher than said first level.
 8. An automatic system as defined in claim 7 wherein said second valve means further includes reopening means for reopening said second valve means in response to pressures in said well conduit above said second pressure level.
 9. An automatic system as defined in claim 7 wherein said second valve means is anchored in said well conduit at a point below said first valve means.
 10. An automatic system as defined in claim 9 wherein: a. said second valve means includes a closure member, a seat member and a self-contained control means; and b. said self-contained control means is connected to said closure member and responsive to said second pressure level to bring said closure and seat members into sealing engagement with each other for blocking flow through said conduit.
 11. An automatic system as defined in claim 9 wherein said first and second valve means are movable through said conduit and include means for retrievably anchoring and sealing said valve means at a subsurface location within said well conduit.
 12. An automatic system as defined in claim 9 wherein said first and second valve means include reopening means for moving said valve means to open position in response to pressure supplied to said well conduit above said valve means.
 13. An automatic system as defined in claim 10 wherein said self-contained control means includes bellows actuator means for opening and closing said closure members to respectively permit or terminate flow through said conduit.
 14. An automatic system as defined in claim 13 wherein said bellows actuator means is linked to said closure member by releasable locking means for operatively disconnecting said closure member from movement of said bellows actuator means in response to pressures in said well conduit above a thiRd pressure level higher than said second pressure level.
 15. An automatic system as defined in claim 14 wherein said bellows actuator means further includes relocking means for reengaging said closure member in response to a reduction of pressure in said conduit to a level below said second pressure level.
 16. An automatic safety valve means for regulating flow through a well conduit comprising: a. closure means movable between open and closed positions for respectively permitting or terminating flow through said conduit; b. movable control means connected through connecting means with said closure means for moving said closure means between open and closed positions; c. closing means included with said control means for closing said closure means when the pressure acting on said control means exceeds a first predetermined value; and d. reopening means included with said control means for reopening said closure means when the pressure acting on said control means is raised above said first pressure value and exceeds a second higher pressure value.
 17. An automatic safety valve means as defined in claim 16 wherein said valve means is movable through said conduit and includes means for retrievably anchoring said valve means at a subsurface location within said well conduit.
 18. An automatic safety valve means as defined in claim 17 further including spring biasing means for urging said closure members toward open position when said closure means are closed.
 19. An automatic safety valve means as defined in claim 17 further including locking means for maintaining said valve closure means in fully opened position while the pressure acting on said control means is below said first pressure value.
 20. An automatic safety valve means as defined in claim 19 wherein said valve means is movable through said conduit and includes means for retrievably anchoring said valve means at a subsurface location within said well conduit.
 21. An automatic safety valve means as defined in claim 20 wherein said control means includes bellows means.
 22. An automatic safety valve means as defined in claim 21 further including incompressible fluids and protective valving means for protecting said bellows means from over contraction and over expansion.
 23. An automatic safety valve means as defined in claim 20 wherein said connecting means includes releasable means for separating said control means from said closure means when the pressure acting on said control means exceeds a second pressure value which is higher than said first value.
 24. An automatic safety valve means as defined in claim 23 further including biasing means operative at pressures in excess of a third pressure value, higher than said second value for returning said closure means to open position when said control means and closure means are separated.
 25. An automatic safety valve means as defined in claim 24 wherein said connecting means further includes reengageable means for reengaging said control means and said closure means when the pressure acting on said control means falls below said first pressure value.
 26. An automatic safety valve means as defined in claim 25 wherein said control means includes bellows means.
 27. An automatic safety valve means as defined in claim 26 further including incompressible fluids and protective valving means for protecting said bellows means from over contraction and over expansion.
 28. A method of remotely or automatically operating first and second valve means and control means anchored in a well conduit at points below the surface of a well, said second valve and control means being anchored in said conduit at a point between said first valve and control means and the surface of said well, comprising the steps of: a. partially or completely closing said well conduit above said first valve and control means; b. allowing the pressure in said conduit to rise to a first pressure level to which said first control means is automatically responsive for closing said first valve means and blocking said conduit; and c. closing said well conduit above said first valve and control means by lowering the pressure in said conduit above said second valve means to a level, below said first pressure level, to which said second control means is automatically responsive to closing said second valve means and blocking said conduit.
 29. A method of controlling flow of well fluids through a well conduit comprising restricting or terminating the flow of well fluid through said conduit at a point above a first subsurface valve which closes in response to a predetermined characteristic of said fluid caused by said restriction or termination of flow, with such method including the prior step of reducing restriction to fluid flow in said conduit at a point above a second subsurface valve which closes in response to a predetermined characteristic of said fluid caused by said restriction reduction, said second valve being located above said first valve whereby said closure of said second valve restricts or terminates fluid flow through said conduit to cause closure of said first valve.
 30. A method as defined in claim 29 including the step of reopening said first and second valves by applying pressure to said conduit above said valve.
 31. A method as defined in claim 29 wherein said first valve closed in response to the flow of fluids through said conduit at a rate below a first predetermined flow rate and said second valve closes in response to the flow of fluids through said conduit at a rate above a second predetermined flow rate, higher than said first rate.
 32. A method as defined in claim 29 wherein said first valve closes when the pressure of fluids in said conduit exceeds a first value and said second valve closes when the fluid pressure drops below a second value, below said first pressure value.
 33. A method of controlling the flow of well fluid through a well conduit comprising restricting or terminating the flow of well fluids through said conduit at a point above a first subsurface valve which closes in response to a predetermined characteristic of said fluids caused by said restriction or termination of flow and reopening said first valve by applying pressure to said conduit from above said first valve.
 34. A method of controlling flow of well fluids through a well conduit comprising restricting or terminating the flow of well fluids through said conduit at a point above a first subsurface valve which closes in response to the flow of fluids through said conduit at a rate below a predetermined minimum flow rate.
 35. A method of controlling flow of well fluids through a well conduit comprising restricting or terminating the flow of well fluids through said conduit at a point above a subsurface valve which closes in response to a predetermined characteristic of said fluids caused by said restriction or termination of flow and reopening said valve by pressurizing said conduit above said closed valve to a pressure in excess of the pressure in said conduit below said valve. 